Oxyalkylene series polymers each having a reactive silicon group are disclosed in JP-A-52-73998 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), U.S. Pat. No. 3,971,751, etc., and a typical example thereof is a polymer represented by the following formula; EQU X".sub.3 Si(oxypropylene polymer)SiX".sub.3
wherein X" represents a hydrolyzable group such as a methoxy group, etc.
A oxyalkylene series polymer having a reactive silicon groups cures by forming a siloxane bond (Si--O--Si) between the polymer molecules by function of moisture in air at room temperature to obtain a rubbery cured material.
Since the cured products exhibit excellent elongation properties, strength, adhesion, etc., the material is used as a sealant, adhesives, so on. The polymer may be used in a form of a composition by mixing with a filler to save material cost. The composition, however, is liable to substantially increase in viscosity, accordingly, a plasticizer is technically essential to be incorporated into the composition.
On the other hand, use of the plasticizer has various problems due to evaporation and shifting the material. For instances, the problems include softening of the composition due to shifting the material to the substrate, causing cracks of the products, softening of a paint when the paint is coated over the products, contamination of the products due to adhesion, and also lowering of the adhesive property and the flexibility of coating with the passage of time, etc.